AMINO ACIDS CLASSIFICATION AND PROPERTIES WHAT ARE AMINO ACIDS.

 Amino acids are organic compounds containing

[- NH2] carboxyl [-COOH] side chain [R group]  The major key elements if amino acids are carbon, hydrogen, nitrogen, oxygen.  About 500 amino acids are known (though only 20 appear in the ) and can be classified in many ways BASIC STRUCTURE[SKELETON]

NEED FOR CLASSIFICATION

 Classification of amino acids gives the grouping between 20 acids and a basic outline for grouping.

 It makes a clear idea to pick the type

 This is much useful for biochemists for the easy understanding between each amino acids. Classification:

Based on  R group  Polarity and R group  Distribution in  Nutritional requirements  Number of amino and carboxylic groups Based on R-Group • Simple amino acids: these have no in their side chain. Example: , , , , • Hydroxy amino acids: these have a hydroxyl group in their side chain Eg: , • Sulfur containing amino acids: have sulfur in their side chain Eg: , • Aromatic amino acids: have benzene ring in their side chain Eg: , • Heterocyclic amino acids: having a side chain ring which possess at least on atom other than carbon Eg: , , • Amine group containing amino acids: derivatives of amino acids in which one of carboxyl group has been transformed into an group Eg: , • Branched chain amino acids: A branched-chain amino acid (BCAA) is an amino acid having aliphatic side-chains with a branch Eg: leucine, isoleucine, valine • Acidic amino acids: have carboxyl group in their side chain Eg: Aspartic and • Basic amino acids: contain amino group in their side chain Eg: , • Imino acid: Amino acids containing a secondary amine group Eg: Proline Polarity and R Group • Amino acids with non polar R group: these are hydrocarbons in nature, hydrophobic, have aliphatic and aromatic groups [aliphatic R groups] Eg: Alanine, Valine, Leucine, Isoleucine, Proline. [Aromatic groups] Eg: Phenylalanine, Tryptophan, Methionine(sulfur) • Amino acids with polar but uncharged R Group: these amino acids are polar and possess neutral pH value. Eg: Glycine, Serine, Threonine, Cysteine, Tyrosine, Glutamine, Asparagine. • Negatively charged amino acids: their side chain [R Group] contain extra carboxyl group with a dissociable proton. And renders electrochemical behaviour to Eg: and Glutamic acid

Aspartic acid • Positively charged amino acid: their side chain have extra amino group Rendering basic nature to protein, Eg: Lysine, Arginine, Histidine.

Lysine Distribution in protein:

• Standard protein amino acids: the amino acids that are used to form proteins, recognized by ribozyme autoaminoacylation systems Eg: Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine • Non standard protein amino acids: these amino acids are not required to build proteins. have a vital role as metabolic intermediates. Eg. , Hydroxylysine, Carboxyglutamate, Diaminopimelate. • Non standard non protein amino acid: These are the derivative of amino acids and have role in metabolism. Eg: Alpha amino butyrate, Citruline, , beta-alanine. Based on nutritional requirements:

• Essential amino acids: Essential amino acids cannot be made by the body. As a result, they must come from food. The essential amino acids are: Arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. • Non essential amino acids: An amino acid that can be made by humans and so is essential to the human diet.

The nonessential amino acids: Alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.

On basis of number of amino and carboxylic groups: Monoamino- monocarboxylic amino acids

• glycine, alanine • proline • phenylalanine • methionine • serine, threonine • Monoamino-dicarboxyli amino acid: Aspartic and glutamic acid • Diamino-monocarboxylic amino acids: Lysine, arginine, histidine. Properties : Physical

• Colourless • Crystalline in nature • Tasteless[tyrosine], sweet[glycine, alanine] • Melting point above 200•C • Soluble in polar solvent and Insoluble in non polar solvent • Have absorbance at 280nm • Mol wt: 100 – 50,000Dt • All amino acids possess optical isomers due to the presence of asymmetric α-carbon atoms. • Some are structurally stable and sterically hindered [Glycine] • Amino acids [proteins]posses enzymatic activities • Amino acids exhibit colloidal nature and denaturing property Chemical properties • Decarboxylation: The amino acids will undergo decarboxylation to form the corresponding “”. Thus amines are produced

• Histidine → Histamine + CO2

• Tyrosine →Tyramine + CO2

• Lysine →Cadaverine + CO2 • Reaction with Ninhydrin: • Reaction with Alkalies (Salt formation): • The carboxyl group of amino acids can release a H+ with the formation of Carboxylate (COO–) .

• Reaction with Alcohols (Esterification) : • the amino acids is reacted with alcohol to form, “Ester”. The esters are volatile in contrast to the form amino acids. • Reaction with DANSYl Chloride: DANSYl chloride means “Dimethyl Amino Naptha Sulphonyl Chloride”. When the amino acid reacts with DANSYl chloride reagent, it gives a “Flourescent DANSYl derivative

• Reaction with acylating agents (Acylation): When the amino acids react with “Acid chloride” and acid anhydride in alkaline medium it gives “pthaloyl amino acid • Reaction with Sanger’s reagent: • “1-flouro-2,4-dinitrobenzene” is called Sanger’s reagent (FDNB).sanger’s reagent reacts with α-amino acid to produce Yellow coloured derivative, DNB-amino acid. • Reaction with Edmann’s reagent: Edmann’s reagent is “phenylisothiocyanate”. When amino acids react with Edmann’s reagent it gives “phenyl thiohydantoic acid” finally it turns into cyclized form “Phenyl thiohydantoin” (Edmann’s derivative). • Reference : Dr. J.L. Jain – Fundamentals of by Chand publications, New Delhi.